1. Field of the Invention
The present invention concerns a method for controlling a print head of the type operating with a number of printing elements according to the thermotransfer principle, in which method an energy quantity to be supplied to a printing element in a first supply step is determined in a determination step, the energy quantity being supplied to the printing element in order to transfer ink from an ink carrier device associated with the print head onto a substrate associated with the ink carrier device for generation of an image point of a print image. The invention concerns a printer that is suitable for implementation of the inventive method.
2. Description of the Prior Art
In order to obtain a qualitatively high-grade image in such thermotransfer printers known, for example, from EP 0 536 526 A2, each printing element of the print head must be supplied with a relatively precisely quantified energy in order to reliably melt the ink particles from the carrier material of the ink ribbon to the desired quantity or spatial expansion. Depending on the current temperature of the respective printing element, more or less energy must be supplied in order to achieve the optimal melting temperature.
The control of the printing elements is normally optimized at the factory for a specific ink ribbon type with a specific ink. To determine the required energy quantity for a respective image point (pixel) of the print image to be generated, a predetermined determination algorithm and a correspondingly set print parameter set are normally used.
A problem is that different requirements for the consistency [quality; condition] of the image points generated on the substrate exist for different types of print images. Particularly for images known as two-dimensional barcodes, high requirements exist for sharpness and contrast in the region of the edges of the rectangles or squares generated via the image points. This applies both in the printing direction and transversely thereto. By contrast, these strict requirements typically exist only in one direction (normally the printing direction) in images known as one-dimensional barcodes. Other requirements must be set for text or free graphics.
In order to satisfy these different requirements to the greatest extent possible, a compromise solution or a solution matched to a specific print image type is selected, but this leads to less satisfactory results, for example in regions of a mixed print image with different print image types.
Alternatively, it is possible to set an activation of the print head used for all print image types, this activation supplying a satisfactory result for the print image type with the highest requirements. From an economic point of view, however, this is normally undesirable because an increased expenditure occurs in regions with lesser requirements.